Scilab Home page | Wiki | Bug tracker | Forge | Mailing list archives | ATOMS | File exchange
Change language to: English - Français - 日本語 - Русский

# syredi

Design of iir filters, syredi code interface

### Syntax

`[fact,b2,b1,b0,c1,c0,zzeros,zpoles]=syredi(ityp,iapro,om,deltap,deltas)`

### Arguments

itype

integer, the filter type: 1 stands for low-pass, 2 for high-pass, 3 for band-pass, 4 for stop-band.

iappro

integer, the design approximation type: 1 stands for butterworth, 2 for elliptic, 3 for Chebytchev1, 4 for Chebytchev2.

om

4-vector of cutoff frequencies (in radians) `om=[om1,om2,om3,om4]`,

```0<= om1 <= om2 <= om3 <= om4 <= pi``` .

When `ftype`='lp' or `'hp'`, `om3` and `om4` are not used and may be set to 0.

deltap

a real scalar, the ripple in the passband. ```0< deltap <1```

deltas

a real scalar, the ripple in the stopband. ```0< deltas <1```

gain

scalar, the filter gain

b2

real row vector, degree 2 coefficients of numerators.

b1

real row vector, degree 1 coefficients of numerators.

b0

real row vector, degree 0 coefficients of numerators.

c1

real row vector, degree 1 coefficients of denominators.

c0

real row vector, degree 0 coefficients of denominators.

zzeros

complex row vector, filter zeros in the z-domain

zpoles

complex row vector, filter poles in the z-domain

### Description

Computes iir filter approximation. The result is given as a set of second order transfer functions `Hi=(b0(i)+b1(i)*z+b2(i)*z^2)/(c0(i)+c1(i)*z+z^2)` and also as a poles, zeros, gain representation.

The filter obtained is `h=fact*H1*...*Hn`.

### Remark

This built-in function is mainly intended to be used by the eqiir function.

### References

The syredi code is derived from doredi package written by Guenter F. Dehner, Institut fuer Nachrichtentechnik Universitaet Erlangen-Nuernberg, Germany.

Dehner,G.F. 1979, DOREDI: Program for Design and Optimization of REcursive DIgital filters-Programs for Digital Signal Processing, ed:Digital Signal Processing committee of IEEE Acoustics, Speech and Signal Processing Society.

For DOREDI.f source code see http://michaelgellis.tripod.com/dsp/pgm25.html

### Examples

```[fact,b2,b1,b0,c1,c0,zzeros,zpoles]=syredi(1,4,[2*%pi/10,4*%pi/10,0,0],0.02,0.001);
h=fact*(b0+b1*%z+b2*%z^2)./(c0+c1*%z+%z^2)```